1. Field of the Invention
The present invention is directed to an electrode arrangement for a medical apparatus for in vivo stimulation of tissue with electrical energy, and in particular to an electrode arrangement of the type having a flat electrode with a large electrode area, which is electrically coupled to an electrode catheter lead, and having a fixing device for attaching the electrode to tissue.
2. Description of the Prior Art
A cardiac electrode arrangement is disclosed U.S. Pat. No. 4,355,642 which has a relatively thick disk-shaped base which supports a first electrode in the form of a spike, and a second electrode in the form of a helix, with a sharp tip, surrounding the spike. The electrode arrangement is affixed to the epicardium by screwing the entire disk-shaped base into the cardiac tissue, by rotation of the entire disk-shaped base until the flat surface of the base comes into contact with the epicardium. Electrical discharge occurs in the cardiac tissue between the tip of the helix and the tip of the spike. In another embodiment, a third electrode in the form of a ring is provided on the disk-shaped base, the ring surrounding the helix electrode.
In order for this known electrode device to be attached to the heart, the patient must undergo thoracic surgery, by which the chest is opened to expose the heart. The electrode can only be affixed to the exposed portion of the heart. Moreover, screwing the electrode into the heart is traumatic to heart tissue, and leads to the formation of scar tissue in the epicardium. Moreover, the electrode must be correctly situated before the screwing the helix into the epicardium since the electrode arrangement cannot be subsequently moved without damage to the heart tissue.
Moreover, since the disk-shaped base is relatively thick in relation to its area, the electrode arrangement is stiff, and therefore cannot conform to the exterior of the heart and is thus unable to assume a relatively large area enabling transmission of a pulse to the largest possible portion of the heart. Since the electrode arrangement is screwed into the epicardium by being rotated until the surface of the base element comes into contact with the heart tissue, the orientation of the electrode arrangement relative to the heart tissue is governed by the operation of screwing the electrode arrangement into the epicardium. The electrode arrangement must therefore have a rotationally symmetrical surface, at least in terms of its electrically conductive elements.
An epicardial pacing electrode is disclosed in U.S. Pat. No. 3,737,579 having an electrode catheter, with a helical electrode mounted at a right angle to the longitudinal axis of the catheter, and Dacron.RTM. webbing disposed substantially perpendicularly to the longitudinal axis. With the aid of a special, substantially tubular tool, into which the pacing electrode arrangement is inserted with the helix pointing in the direction of the longitudinal axis of the tool, the helix can be screwed into the heart by rotating the tool until the Dacron.RTM. webbing comes into contact with heart tissue. The electrode can be additionally affixed by suturing the Dacron.RTM. webbing to the heart.
In this known device, the electrode area is small, as is standard for a pacing electrode, however, the device could not be modified to significantly increase the electrode area, because the electrode arrangement is screwed at a right angle into heart tissue. As a result of the fixed helix in this known pacing electrode, electrode fixing and orientation with respect to the heart are performed simultaneously. Orientation of the electrode arrangement thus arises directly from the fixing operation, so that the position of the electrode after the helix has been screwed into the heart tissue cannot be altered. This means that the electrode catheter could ultimately extend upwardly or downwardly after implantation, with the ultimate orientation of the catheter not being able to be determined in advance because that orientation is a function of the extent to which the helix is screwed into the cardiac tissue.
A defibrillator electrode arrangement is disclosed in European Patent 0 211 166 containing a plurality of individual electrodes. Each electrode has a fixing plate with a helix for affixing that electrode to the heart. The tip of the helix points at a right angle relative to the longitudinal axis of the catheter. A plurality of coiled conductors are disposed around the fixing plate, these conductors forming the active electrode surface. For implantation, a tool is used similar to that employed in the aforementioned U.S. Pat. No. 3,737,579. The tool is connected to the fixing plate with the helix oriented so that when the tool is rotated, the helix is screwed into the heart tissue until the surface of the fixing plate comes into contact with the heart. The coiled electrode conductors are, during implantation, raised from the fixing plate and are held along the exterior of the tool with needles respectively disposed at the ends of the coiled conductors. When the fixing plate is screwed into place, the coiled electrode conductors are detached from the tool, and are applied to the heart tissue and affixed thereto using the needles. After all of the electrodes have been attached to the heart, they are interconnected with a common electrode catheter.
In this known electrode arrangement, a plurality of electrodes is used to cover a large part of the heart tissue, thus making more comprehensive implantation surgery necessary. The large number of electrodes also results in a large number of lesions on the heart tissue, thereby increasing the risk of post-operative complications. Moreover, the electrodes must be symmetrical, for the same reason discussed above with regard to other known electrode arrangements. The fixing plate is stiff, and the direction of the electrode catheters in the implanted position cannot be determined in advance, thereby increasing the difficulty in interconnecting the individual electrode catheters to the common electrode catheter.
For endocardial electrode arrangements, the use of a movable helix for attaching an electrode to heart tissue is known. One such electrode arrangement is described in U.S. Pat. No. 4,311,153. During introduction into the heart, the helix is enclosed in a sleeve which constitutes a part of the electrode catheter so that no tissue is damaged. The sleeve is coated with a membrane to prevent the entry of body fluids. Inside the heart, the helix is advanced to affix the electrode to endocardial tissue. The helix is advanced in a direction along the longitudinal axis of the electrode catheter by rotation of a connection contact attached to the helix, or by means of a detachable stylet inside the electrode catheter.
Another known endocardial electrode arrangement is described in U.S. Pat. No. 4,922,927, and contains a defibrillation electrode extending the length of an electrode catheter, and a pacing electrode at the end of the electrode catheter. A movable helix is attached to the end of the catheter at which the pacing electrode is disposed. During implantation of the electrode arrangement, the helix can be manipulated with a stylet so it rotates around an axis parallel to the longitudinal axis of the electrode catheter, and can thereby be screwed into heart tissue for fixing the electrode arrangement. The electrode arrangement can be removed from the tissue if the screw is rotated in the opposite direction.
As noted, the axis of rotation of the helix in both of the above known endocardial electrode arrangements is parallel to the axis of the electrode catheter, so that the electrode devices can be pressed against heart tissue during implantation as the helix is screwed into the tissue, thereby ensuring a firm seating of the helix, even though the helix is remotely manipulated. The same result is obtained in the epicardial electrode arrangements for which a tool is employed for aiming the helix at the heart tissue and for rotating the entire electrode.